U.S. patent application Ser. No. 904,421, filed May 10, 1978 and now U.S. Pat. No. 4,209,905 issued July 1, 1980, by the present applicant, discloses the use of magnet elements for retaining dentures in place. Paired magnet elements are employed, one element of a pair being embedded in the denture and the other element being located in a support associated with the wearer's jawbone. As described in the patent application, the support might comprise a decoronated natural tooth or a dental implant.
In accordance with a preferred aspect of the invention disclosed in the earlier patent application, an inverted U-shaped magnet element is located in the denture and a magnetisable element (rather than a magnet as such) is located in or on a tooth stump which is to be engaged by the denture. When the denture is fitted, pole faces of the magnet abut the magnetisable element so that the magnetisable element bridges the pole faces in the manner of a keeper and so that a closed-loop magnetic circuit is established. Abutment of the magnet and the magnetisable elements is effected for the purpose of establishing maximum retentivity, and a closed loop magnetic circuit is proposed in the interest of reducing leakage flux to the lowest possible order.
However, the establishment of abutting contact between the magnet and magnetisable elements requires that the pole faces at least of the magnet be exposed, and it is now thought by the Inventor that there may be merit in protecting the magnet pole faces against corrosion induced by the oral environment and/or against physical damage to the magnet element.